Introduction to 8085 Microprocessor (μP)

Summary

This educational video introduces the concept of word length in microprocessors, focusing on the Intel 4004, the first 4-bit microprocessor introduced in 1971. It explains how the 4-bit word length allows for processing, input, and output of 4-bit data chunks, performing 4-bit additions, and using place values for unsigned and signed representations. The video also covers the evolution to 8-bit microprocessors like the Intel 8085, highlighting their expanded range of numbers due to increased word length.

Takeaways

• 😀 The 8085 microprocessor is the focus of the session, with an introduction to its capabilities and specifications.
• 📚 The word length of a microprocessor is defined as the size of data it can handle at once, which is a key characteristic of its processing power.
• 🛠️ The Intel 4004, introduced in 1971, was a 4-bit microprocessor, meaning it could process four bits of data simultaneously, including performing 4-bit additions.
• 🔢 The place values for a 4-bit microprocessor in unsigned representation are 1 (2^0), 2 (2^1), 4 (2^2), and 8 (2^3), allowing it to represent numbers from 0 to 15.
• 💡 The Intel 4004 could only perform addition and subtraction within the range of 0 to 15 for unsigned numbers due to its 4-bit word length.
• ➕ In binary addition, a carry is generated when the sum of bits exceeds the bit capacity, which is then added to the next significant bit.
• 🚫 The Intel 4004 cannot perform operations resulting in numbers outside its 4-bit range, such as adding 8 and 9, which would result in 17.
• 🔄 The 4-bit microprocessor uses two's complement for subtraction, where the negative inverse of a number is found by inverting the bits and adding one.
• 🔢 In two's complement representation, the place values for a 4-bit microprocessor are 1, 2, 4, and -8, allowing it to represent numbers from -8 to 7.
• 🔄 The most significant bit in signed representation has a negative place value, affecting the range of numbers the microprocessor can represent.
• 📈 The evolution of microprocessors is highlighted, with the Intel 8085 being an 8-bit microprocessor capable of handling larger data sets and more complex operations than its 4-bit predecessors.

Q & A

What is the word length of a microprocessor?

The word length of a microprocessor is the size of data it can handle at once, measured in bits.

What was the word length of the Intel 4004 microprocessor?

The Intel 4004 microprocessor, introduced in 1971, had a word length of 4 bits.

How did the Intel 4004 perform 4-bit addition?

The Intel 4004 performed 4-bit addition by taking two 4-bit inputs, processing them, and generating a 4-bit output, including handling carry operations.

What is the range of values that can be represented with a 4-bit unsigned representation?

With a 4-bit unsigned representation, the range of values is from 0 to 15.

How does the Intel 4004 handle subtraction?

The Intel 4004 handles subtraction using the two's complement technique, effectively performing addition of the minuend and the two's complement of the subtrahend.

What is the two's complement of a binary number?

The two's complement of a binary number is found by inverting all the bits of the number and then adding one to the result.

What is the range of values that can be represented with a 4-bit sign representation?

With a 4-bit sign representation, the range of values is from -8 to +7.

What is the significance of the most significant bit in sign representation?

In sign representation, the most significant bit indicates the sign of the number, with 0 typically representing positive and 1 representing negative.

What is the difference between unsigned and sign representation in a microprocessor?

Unsigned representation uses all bits to represent the magnitude of a number, while sign representation uses the most significant bit to indicate the sign of the number, with the remaining bits representing the magnitude.

Why is the range of values different for unsigned and sign representations in a microprocessor?

The range is different because unsigned representation uses all bits for magnitude, allowing for a larger range of positive values, while sign representation dedicates one bit to indicate the sign, reducing the range of positive and negative values it can represent.

What is the word length of the Intel 8085 microprocessor?

The Intel 8085 microprocessor has a word length of 8 bits.

What range of numbers can the Intel 8085 handle in unsigned representation?

In unsigned representation, the Intel 8085 can handle numbers from 0 to 255 (2^8 - 1).

What range of numbers can the Intel 8085 handle in sign representation?

In sign representation, the Intel 8085 can handle numbers from -128 to +127.

Outlines

00:00

📘 Introduction to the 8085 Microprocessor and Word Length

This paragraph introduces the 8085 microprocessor, focusing on its word length, which is the amount of data it can handle simultaneously. The Intel 44, a 4-bit microprocessor from 1971, is used as an example to explain the concept of word length. The 4-bit word length allows the Intel 44 to process, input, and output data in 4-bit chunks, enabling 4-bit addition operations. The explanation includes a step-by-step addition example using binary numbers, demonstrating how the carry bit is handled during the process. The paragraph also discusses the representation of unsigned numbers using 4 bits, which can range from 0 to 15, and how the least and maximum values are determined.

05:02

🔢 Understanding Binary Addition and the Range of 4-bit Numbers

The paragraph delves into the specifics of binary addition using the Intel 44 microprocessor as a reference. It explains the process of adding 4-bit numbers and the resulting carry bit, using a detailed example of adding two numbers, 101 and 0101, to produce a sum and carry. The explanation includes the place values for 4-bit numbers and how they are used to determine the decimal equivalent of the binary inputs and outputs. The paragraph also discusses the range of values that can be represented with 4 bits in unsigned representation, emphasizing that the Intel 44 can perform unsigned additions within this range.

10:03

🔄 Two's Complement and Binary Subtraction with the Intel 44 Microprocessor

This section explains the concept of two's complement and its application in binary subtraction using the Intel 44 microprocessor. It describes the process of finding the two's complement of a binary number to perform subtraction, using an example where the minuend is 1101 and the subtrahend is 0101. The paragraph details the step-by-step method of toggling bits to find the negative inverse of the subtrahend. It also discusses the place values in two's complement representation, which differ from unsigned representation by having the most significant bit's place value as negative. The example concludes with the addition of 9 and -5 in two's complement, resulting in a difference of 4.

15:06

🔢 Sign Representation and the Range of 4-bit Signed Numbers

The paragraph discusses sign representation in 4-bit binary numbers, explaining how the most significant bit is used to indicate the sign of the number. It details the place values for signed numbers, which include negative values for the most significant bit. The explanation includes a step-by-step calculation of decimal equivalents for various binary sequences, demonstrating how both positive and negative numbers can be represented. The range of values that can be represented with 4-bit sign representation is also discussed, showing that it extends from -8 to +7. The paragraph clarifies the difference between the ordered decimal numbers and the unordered binary bit sequences.

20:09

🚀 Evolution of Microprocessors and the 8085's 8-bit Word Length

The final paragraph summarizes the evolution of microprocessors, mentioning the introduction of the Intel 8008, 8080, and the 8-bit Intel 8085 microprocessor. It highlights the increased word length of the 8085, which allows it to handle 8 bits of data at once. The paragraph outlines the range of numbers that can be represented in both unsigned and signed representations for an 8-bit microprocessor, emphasizing the broader range of values that can be processed compared to the 4-bit Intel 44. The session concludes with a preview of the next topic, which will cover the pins of the 8085 microprocessor.

Keywords

💡8085 Microprocessor

The 8085 Microprocessor is a specific model of microprocessor introduced by Intel in 1977. It is an 8-bit microprocessor, meaning it can handle 8 bits of data at once. In the video, the 8085 is the central topic, and its word length, which is the size of data it can process, is a key aspect discussed. The script explains how the 8085's word length affects its capabilities, such as performing 8-bit additions and subtractions.

💡Word Length

Word length refers to the number of bits a microprocessor can process simultaneously. It is a fundamental characteristic that determines the microprocessor's data handling capacity. The script introduces the concept by discussing the evolution of microprocessors, starting with the 4-bit Intel 44 and moving to the 8-bit Intel 8085, highlighting the increase in word length and its implications for processing power.

💡Unsigned Representation

Unsigned representation is a way of encoding numeric values using binary numbers without considering sign bits. It allows for representing only non-negative integers. The script explains that with a 4-bit unsigned representation, values from 0 to 15 can be represented, which is the range of numbers the Intel 44 microprocessor could handle.

💡Two's Complement

Two's complement is a method used in digital systems to represent signed integers in binary form. It allows for the representation of both positive and negative numbers. The script describes how the Intel 44 microprocessor uses two's complement to perform subtraction by converting the subtrahend to its negative inverse before adding it to the minuend.

💡Binary Addition

Binary addition is the process of adding binary numbers, similar to decimal addition but following the binary system rules, where the base is 2 instead of 10. The script provides an example of binary addition with a 4-bit number, explaining the process of carrying over when the sum of bits exceeds 1.

💡Place Value

In the context of binary numbers, place value refers to the value of a bit based on its position in the number. The script explains the place values for both unsigned and two's complement representations in a 4-bit system, illustrating how these values contribute to the overall decimal equivalent of the binary number.

💡Carry

Carry is a term used in binary addition when the sum of two bits is greater than 1, resulting in an extra bit that must be carried over to the next higher place value. The script demonstrates this concept in the example of adding 4-bit numbers, where a carry is generated and added to the next bit position.

💡Minuend

The minuend is the number from which another number (the subtrahend) is to be subtracted in a subtraction operation. In the script, the term is used in the context of explaining binary subtraction using two's complement, where the minuend is the number being kept and the subtrahend is the number being subtracted.

💡Subtrahend

The subtrahend is the number that is to be subtracted from another number (the minuend) in a subtraction operation. The script discusses how the subtrahend is converted to its two's complement form to perform subtraction using the addition method in binary systems.

💡Sign Representation

Sign representation, also known as signed magnitude representation, is a way of encoding signed numbers in binary form where the most significant bit is used to indicate the sign of the number (positive or negative). The script explains how the Intel 44 microprocessor, with its 4-bit word length, can represent numbers from -8 to +7 using sign representation.

💡Evolution of Microprocessors

The evolution of microprocessors refers to the historical development and technological advancements in microprocessor design. The script outlines the progression from the 4-bit Intel 44 to the 8-bit Intel 8085, emphasizing the increase in word length and the expansion of capabilities such as handling more complex calculations and larger data sets.

Highlights

Introduction to the 8085 microprocessor and its significance in the evolution of microprocessors.

Definition of word length in microprocessors and its importance for data handling capabilities.

Historical context: The Intel 4000 family and the introduction of the 4-bit Intel 44 microprocessor in 1971.

Explanation of 4-bit data handling, including input, processing, and output capabilities of the Intel 44.

Demonstration of 4-bit addition using the Intel 44 microprocessor and its truth table.

Illustration of carry generation and management during 4-bit addition.

Calculation of place values for 4-bit numbers and their decimal equivalents.

Range of unsigned numbers representable with 4 bits, from 0 to 15.

Introduction to two's complement for subtraction in microprocessors.

Process of finding the two's complement of a binary number for subtraction.

Place values in two's complement representation, including negative values.

Example of performing subtraction using two's complement in a 4-bit microprocessor.

Range of signed numbers representable with 4 bits, from -8 to 7.

Comparison between unsigned and signed representations in 4-bit microprocessors.

Transition from 4-bit to 8-bit microprocessors, with the introduction of the Intel 8085.

Explanation of the range of numbers representable in unsigned and signed formats for the 8-bit Intel 8085 microprocessor.

Summary of the session on the word length of microprocessors and预告of the next session on the pins of the 8085 microprocessor.

Transcripts

[Music]

hello everyone and welcome to the

chapter fundamentals of 8085

microprocessor so this is the first

session of our new chapter and in this

session we will be introduced to the

8085

microprocessor so without any further

Ado let's get to

learning coming to the topic that we are

going to cover today today we will try

to understand what is the word length of

microprocessor so the word length of a

microprocessor is the size of data which

the microprocessor can handle at once if

you remember when we were learning about

the evolution of microprocessor we

learned that in 1971 as a member of the

Intel 4000 family

44 that is the first microprocessor was

introduced now if you remember the word

length of this was 4 bit now what is

meant by that

the Intel 44 microprocessor could handle

four bits of data at once that is it can

take a chunk of 4bit as input it can

process that 4bit chunk also it can

generate a 4bit output now since the

word length of Intel 44 was 4bit

therefore it can perform 4bit additions

now in the previous session we have seen

the truth table for addition use using

this logic inel

44 since it has the word length of 4bit

could perform 4bit addition so clearly

if we feed the aent as 1 01 and if we

also feed the addent 01 01 until 404

could perform the addition let's Now

quickly perform the addition for it 1 +

1 is supposed to generate the sum as Zer

and the carry as one so we are going to

have the sum as zero now what will be

done with the carry well the place value

of these two bits is 2 ra to the^ 0 and

the result which is just generated by

performing the addition between these

two is actually one Zer that is a two

bit number so the carry will be added

with the bits in the 2 ra to the power

one's place so adding one with zero we

will get one also if we again add that

one with 0o we will receive the sum as

one isn't it so no carry only the sum as

one because we are adding one with zero

and that to twice let's move on to the

next unit 0 + 1 we are supposed to get

the result as 1 right finally adding one

with zero we will again get the result

as one let's now check whether we have

perform the addition correctly or not

and for that we will be needing the

place values now if you notice the aent

addent and also the result all are of

four bits now for four bits what will be

the place values well 1 2 4 and 8 to be

precise 2 ra to the^ 0 that is 1 2 ra to

the^ 1 that is 2 2 squar that is 4 and

finally 2 cubed that is 8 now

considering these wets what is the

decimal equivalent value of the aent

well 8 + 1 that is 9 what about the

addent 4 + 1 that is 5 let's move on to

the result now 8 + 4 that is 12 + 2 will

give us 14 and yes it is correct because

9 + 5 is

14 now focus on the weights with these

wordss we can only represent unsigned

numbers so these are used for unsigned

representation now think about it if we

talk about unsigned representation we

are going to use the place values 1 2 4

and 8 to be precise 2 ra to the^ 0 2 ra

to the^ 1 2^ 2 and 2 Cube now with four

bits how many sequences can we have well

we will begin with 0 0 0 0 then 0 0 0 1

so on and at last we will have 1 1 1 1

that is from four zeros to 4 1es now if

we also consider the equivalent decimal

values 0 0 0 0 is 0 then we will have 1

2 3 4 5 and so on and the last value

that is all ones will be

15 so using four bits we can represent

the values from 0 to 15 and all of these

are positive values that is

unsigned now from this particular list

can you figure out the least number well

it is zero right so if we are talking

about the range with four bits with

unsigned representation that is using

these place values the least number that

we can have is zero now what is the max

number it is 15 and how did we get it we

got it by placing all ones underneath

these place

values now for four bits I already have

told you multiple times what are the

actual place values 2 ra to the^ 0 2 ra

to the^ 1 2^ 2 2 Cub now think about the

next place if we had that place what

would have been the place value 2 ra to

the power 4 right and what is 2 ra to

the^ 4 it is

16 and we got the maximum number in this

list as 15 that is 1 less than the next

place value so in order to define the

range from the least value which is zero

we can have the max value that is 2 to ^

4 - 1 or in other words 16 - 1 that is

15 now you could ask me why we are using

this particular notation why can't we

write 15 instead well we can there is

nothing wrong about it but it's a

generalized formula why because in case

of five bits if we just Place five in

this place we will have the maximum

number of five bits using unsigned

representation and it's also meaningful

since we are using four bits so we will

only have to place the number of bits in

here is it clear so this is the range

for four bit numbers using unsign

representation now focus on the Range it

is 0 to 2 to ^ 4 -1 and we are talking

about the unsigned

representation so if we talk about the

number line we are having the range from

0 to 15 and all these 16 numbers we are

representing using the binary sequences

starting from 0 0 0 0 0 0 0 1 till all

ones that is four ones so the Intel 4004

since it has the word length of four bit

it can perform unsigned additions of two

4bit numbers which will involve both the

aent and the addent from this particular

list Additionally the result or the

outcome will also have to be from this

list only for an instance if we add 5

which in binary is 0 1 0 1 with 10 that

is 1 1 0 the result is going to be 15 or

1111 and this can be done since 11 1 1

is a 4bit binary number and additions as

such can be performed by Intel 44 4bit

micro processor however if we add 8 with

N9 that is if we add 1 tri0 with 1

01 the result is going to be 17 which is

not in this particular range so this

microprocessor is not going to produce

that result I hope the word length for

addition is clear to you now like this

Intel 4004 can also perform

subtraction now if you remember when we

learned about the subtraction in binary

we learned about two different

approaches one the pen and paper method

and on the other hand we learned about

the machine's approach therefore when we

are talking about subtraction performed

by the 44 4bit microprocessor it is

going to take this approach under

consideration and specifically it will

perform the subtractions using tw's

complement technique

let me show you one such subtraction

where we are going to have the minu end

as one1 and the subtra this time is 0 1

01 now as I told you earlier we are not

going to perform a minus B rather we are

going to perform A+ minus B because

that's how using addition we can also

perform subtraction which is followed in

both ones and two's complement

approaches now here we have got the B

that is the subtend at as 0 1 0 1 now in

order to get the negative inverse

remember we are implementing two's

complement just like the 44 4bit

microprocessor so we will find out the b

complement that is a negative inverse of

B and for that how to do it if you

remember the technique for tw's

complement we are going to Traverse the

subtend from the least significant bit

towards the most significant bit and we

will keep retaining the data until we

encounter one once we encounter one we

will retain it as it is however the rest

of the bits are going to be toggled that

is zero will become one and one is going

to be zero so finally in case of the

most significant bit we toggled it to

one so this is the two's complement of

the subtend 01 01 now we have discussed

about the conversion process but I

didn't tell you what is happening in

here in reality that is how it is min -

5 because if we consider 01 0 1 it is 5

and negative inverse of that is supposed

to be minus 5 right now we just have

observed the place values in case of

unsigned representation for four bit now

since we are talking about these numbers

what is going to be the place values in

two's complement the place values are 1

2

4 and minus 8 that is apart from the

most significant bed all the remaining

places have the same place values only

the most significant bit has the place

value in

negative now look at

this 1 1 1 that is - 8 + 2 which will

give us - 6 + 1 that is we are adding -

6 with 1 we will get

-5 now you get it how did we get minus5

well the place value of the most

significant bear is Min -

A remember this is for four bits in case

of five bits apart from the most

significant bit the rest of the bits

will have the same place values just

like unsigned representation however the

most significant bit is going to have

the place value minus 16 because we are

talking about five bits then since we

are dealing with four bits in here for

four bits the most significant bits

place value is 8 that is 2 Cub which in

case of two's complement approach is - 8

or -2 to^ 3 or - 2

Cub now with - 5 if we add 1 0 0 1 now

here do remember this is in unsigned

representation so it is going to be 9

because here the place value is 8 only

so 8 + 1 is going to give us 9 now let's

observe if we add these two what is

going to be the result 1 + 1 will give

us the sum as zero and the carry is

going to be 1 1 + 0 is 1 then 1 + 1 will

again give us the sum as 0o and the

carry is going to be one now adding one

with all these zeros we will receive the

sum as one now what about the most

significant bits 1 + 1 will give us 1 Z

remember we are performing the

subtraction in two's complement

therefore whenever the carry is

generated we are going to discard it now

consider the result it is 0 1 0 0 what

is the place value of this one it is

four and yes from nine if we subtract 5

we are getting four however we didn't

perform subtraction this time rather we

added 9 with minus 5 and got the

difference as four now let's focus on

the negative

inverse we got this value - 5 using S

representation now in case of sign

presentation since we are talking about

four bits the place values are going to

be 1 2 4 - 8 remember whenever we are

talking about sign representation

whatever the number of bits may be the

most significant bit will always have

the place value in

negative now just for a moment forget

about these signs just think about it we

are using four bits now with four bits

how many binary sequences can we have

well starting from all zeros till all

ones there is 16 different

sequences let's now try to find out the

equivalent decimal numbers although this

time we are going to consider these

place

values now if you notice these patterns

till this particular point we haven't

placed one in the most significant bits

place so till this point the decimal

equivalence will be the same as we had

in case of unsigned numbers that is from

0 to

7 now once we have placed one in the

most significant bits place of the sign

representation considering the place

value what is going to be the decimal

equivalent well minus 8 isn't it now

what about the next sequence -8 + 1 that

is - 7 focus on the next sequence -8 + 2

that is - 6 then - 8 + 2 that is - 6 + 1

that is - 5 which we already used didn't

we now what about the next sequence -8 +

4 that is

-4 then -8 + 4 that is -4 and with -4 if

we add 1 we will get

-3 focus on the next sequence - 8 + 4

that is -4 + 2 that is

-2 now what about the last sequence 1 1

1 1 1 - 8 + 7 because 3 1's is 7 right

that is

min-1 now from all these decimal values

can you figure out the minimum and the

maximum

values well the minimum value is min - 8

right now what is the maximum value it

is 7even that is + 7 or postive 7 so

clearly with the sign representation of

four piit

we can represent from -8 till

pos7 now what is - 8 this is actually -

2 Cub however since we are considering

four bits we can also state it as - 2 to

^ 4 - 1 notice - 2 cubed 4 - 1 is 3 so

from -2 ra to^ 4 - 1 that is - 8 using

four bits sign representation we could

represent till the maximum value that is

seven and how did we get this we got

this by adding all these ones place

values now what is seven it is 1 less

than 8 so we could also write 7 as 2 ra

to the^ 4 - 1 - 1 that is 2 cubed or 8

-1 so this is the range for 4 bit sign

represent

resentation now we just also have seen

the unsigned representations range it

was from 0 to

15 and we use the sequence from all

zeros that is four zeros to 4 ones to

represent this particular

range now when we are talking about the

sign representation here the most

significant bits they represent the

negative

weightage so the range is not going to

be this anymore rather we will have - 8

- 7 - 6 - 5 -4 -3 - 2

-1 now if you notice this particular

line this is wrong from our perspective

because we deal in decimal number

systems right so if we want to represent

the range that is from - 2 to^ 4 - 1 to

2^ 4 - 1 - 1 we should re arrange this

that is - 2 to ^ 4 -1 or - 2 cubed or -

8 and 2 to ^ 4 - 1 - 1 that is 2 cubed -

1 or 8 - 1 that is

7 now notice the decimal numbers are

organized that is we are having the

least value as -8 and the maximum value

is + 7 however now we don't have the

order in the binary bit

sequences so remember Intel 44 4bit

microprocessor if it used sign

representation could deal with the numb

starting from minus 8 that is 1 0 till

the positive number + 7 that is 0le

1 and that's the buy of the W length of

4 bit so to sum it up we could say in 44

4bit mu p in unsigned representation

could use the numbers starting from 0

till 2 to ^ 4 - 1 that is from 0 to 15

16 - 1 that is 15 now coming to sign

representation it could deal with the

values from - 2 to^ 4 - 1 till 2 to ^ 4

- 1 - 1 that is from - 2 cubed or - 8

till 2 cubed - 1 or POS 7 remember this

all these exponents are four because the

word length of 44 was 4

bit now during the evolution of

microprocessors we have learned in

1972 Intel introduced the next

microprocessor that is Intel

8008 in 1974 it introduced Intel

880 and then in 1977 Intel came up with

intel 80 85 notice this is an 8bit

microprocessor in other words it has the

word length of 8 bit so if we follow

this particular format we could say

intel

8085 if we talk about the unsigned

representation can deal with the range

of numbers from 0 to to ra to the^ 8

minus one and similarly following this

for the 8bit microprocessor in

8085 we can also say for sign

representation it can deal with the

numbers within the range - 2 ra to^ 8 -1

2 2 to ^ 8 -1

-1 and we are having these ranges of

both unsigned and signed representation

due to the word length 8

bit in other words Intel

8085 can deal with 8 Bits of data at

once

also feel free to write down the ranges

in decimal for these two representations

in the comment

section so in this session we covered

the topic word length of

microprocessor all right people that

will be all for this session in the next

session we are going to learn about the

pins of 8085 microprocessor so I hope to

see you in the next one thank you all

for

watching

[Music]